Electron gun



R. E- BENWAY Jan. 5, 1965 ELECTRON GUN 2 Sheets-$heet 1 Filed Dec. 21, 1960 MW mm M 7 my M K Jan. 5, 1965 R. E. BENWAY 3,164,426

ELECTRON GUN Filed Dec. 21, 1960 2 Sheets-Sheet 2 I I I I I I I I I I I I C INVENTOR. #055675 fn/n/Ar United States Patent 3,164,426 ELECTRON GUN Robert E. Benway, Marion, Ind, assignor to Radio Corporation of America, a corporation of Delaware Filed Dec. 21, 196i), Ser. No. 77,446 3 Claims (Cl. 31382) This invention relates to electron guns such as are used in cathode ray tubes and particularly to a novel electrode assembly therefore.

In one prior art type of electron gun two subassemblies are joined together to form a completed gun. One subassembly, referred to as a cathode-control grid subassembly, includes a cathode and a control grid. The cathode and control grid are usually concentric tubular members which are mounted between a pair of spaced insulator plates, such as mica, and which have their longitudinal axes disposed transversely to the path of the electron beam. The other subassembly, referred to as a focusing subassembly, includes a screen grid cup having an electron beam aperture in the end wall thereof and other tubular focusing electrodes coaxial therewith, all supported in spaced relation along a pair of electrical insulator rods.

The tubular control grid is provided with an electron beam aperture in the side wall thereof and the flat elongated tubular cathode, coaxially disposed within the control grid, has an electron emissive surface coating op posite the control grid aperture. Electrode support members disposed alongside tubular control grid and elongated cathode are also mounted between the two spaced parallel mica insulator plates.

A completed electron gun comprising the two subassemblies is provided by aligning the electron beam apertures of the screen grid cup and the tubular control grid and then fixing the screen grid cup to the two electrode support means of the cathode-control grid subassembly. Such joinder of the two subassemblies may be facilitated by use of a metal plate which spans the two support means and which is provided with a large aperture for receiving the screen grid cup. In the electron gun thus formed, the axes of the tubular control grid and cathode are transverse to the axis of the focusing subassembly and to the axis of the electron beam produced by the gun.

In joining the two subassemblies to form the completed electron gun, the electron beam apertures of the screen grid cup and the tubulm control grid must be precisely aligned. The alignment of these two apertures is critical and difficult to obtain. In prior art guns of the type described, the fact that the screen grid cup and tubular control grid electrodes are included in diiferentsubassernblies gives rise to difiiculties of assembly and frequently results in inaccuracies of alignment.

It is preferred that the control grid and screen grid apertures be aligned directly rather than aligning other predetermined surfaces which have established spaced relationship thereto. For example, in guns where two apertures are easily accessible, they are preferably aligned by inserting a small stiff mandrel rod directly into the apertures. However, in the prior art gun of the type descibed above, this method of aperture alignment is not practical since the two apertures are not easily accessible from either end. The cathode blocks accessibility from one direction, and the presence of the other tubular electrodes in the subassembly containing the screen grid cup interferes with the aligning of the apertures from the other direction.

It has been proposed to align the two subassernblies of the above-described prior art gun by providing additional holes through the tubular control grid and screen grid cup which are not obstructed by the cathode and then align these on a mandrel. However, accuracy of align- SJMAZB Patented Jan. 5., 1%65 ment by such a method depends upon a precise relationship of these alignment holes With the electron beam apertures of both electrodes. This feature, thus, also contributes to the possibility of inaccurate alignment. Furthermore, in prior art guns of the type above-described, the cathode-control grid subassembly is not as rigid as is desired for maintaining aperture alignment when once it is obtained.

It is therefore an object of my invention to provide a new and improved electron gun of the above-described type in which the two subass'emblies can be more easily and accurately aligned and which is more rugged than prior art guns of the same general type.

It is another object of my invention to-provide a new and improved electron gun in which the control grid and screen grid apertures can be aligned and fixed relative to each other prior to the assembly of the rest of the gun.

It is another object of my invention to provide a new and improved electron gun of the general type abovedescribed in which the screen grid and control grid apertures are easily accessible for direct alignment either by insertion of a mandrel therein or by use of optical equip ment, either. of which can be operably disposed in close proximity to the two apertures so as to minimize or reduce the possibility of alignment inaccuracy.

It is a further object of my invention to provide a new and improved electron gun of generally the abovedescribed type which comprises fewer parts and which is thusflless costly, simpler to fabricate, and more rugged than prior art guns of the same general type.

Briefly, according to my invention an electron gun includes a first subassembly which comprises an elongated electrode support member which may be of channelshaped transverse section, a tubular control grid disposed therein, and an elongated cathode disposed in the tubular control grid, all three of which are mounted in parallelspaced relation between two spaced insulator plates, preferably of mica. The control grid has an electron beam aperture in the side wall thereof facing out of the channel. An electrode plate, also included as part of the. first subassembly, is mounted on the channel member across the open side thereof and has an electron beam aperture therein aligned with the control grid aperture. The electrode plate constitutes the apertured end wall portion of a 2-piece screen grid cup. The tubular por-' tion of the screen grid cup is included as part of a second subassembly which also includes other tubular electrodes mounted in coaxially spaced relationalong an insulator rod.

According to my invention the screen grid cup is provided in two parts, one part being included with each of the two different subassemblies of the electron gun. By virtue of such an assembly alignment of the screen grid and control grid apertures is facilitated because of their accessibility and because they can be aligned before the two subassemblies are joined together. The tubular portion of the screen grid cup is fixed in a simple manner, e.g., by welding to the apertured portion of the screen grid cup after the screen grid and control grid apertures are aligned.

In the drawings:

FIG. 1 is a side elevational view with parts broken away of a portion of a cathode ray tube incorporating the electron gun according to my invention;

FIG. 2 is an exploded perspective .view of a portion of the electron gun of FIG. 1;

FIG. 3 is a longitudinal sectional view of the electron gun parts in FIG. 2 in their assembled relationship; and

FIG. 4 is a longitudinal sectional view of a portion of the electron gun of FIG. 1 illustrating aperture alignment of the control and screen grids by use of a mandrel.

In PEG. 1 a cathode ray tube having a tubular neck Section 10, funnel section 11, and a faceplate 12 are shown. An electron gun 14 is disposed in the neck section and is adapted to project an electron beam therefrom, and through the funnel 111 to the faceplate 12 which is transversely disposed in the beam path, and on which a luminescent screen 15 is deposited.

The electron gun 14 comprises a cathode-grid-apertured-plate subassembly i6 and a focusing subassembly 18. The cathode-grid-apertured-plate subassembly 16 (see also FIG. 2) includes, in addition to the cathode and control grid electrodes, an apertured plate-like member 20 which constitutes the apertured end wall portion of a screen grid cup 22. A tubular elementl l included as part of the focusing subassembly 18 con stitutes the tubular portion of the screen grid cup 2 2. The focusing subassembly 18 also includes tubular focusing and accelerating electrodes 26 and 28, respectively (shown only in FIG. 1) which, together with the tubular screen grid element 24- are mounted in coaxially spaced relation on a plurality of insulator rods 30. The electrodes 24, 26, and 23 are mounted on the insulator rods by U-shaped studs 32 which are fixed to the electrodes and bonded into the insulator rods 30. The two subassemblies 16 and 18 are integrated to form the complete gun 14 by coaxially fixing together, such as by welding, the two screen grid cup parts 2t) and 24. As is described hereafter in greater detail with reference to FIGS. 2 and 3, these two screen grid parts are preferably specifically shaped so that they mate together in self-aligning relationship. The electron gun i4 is so supported'within the neck lltl (FIG. 1) that the cathodegrid-apertured-plate subassembly 16, which contains the precisely aligned control and screen grid apertures, bears no weight or strain other than its own. The focusing subassernbly 18 is supported within the neck it) by connection of the studs 32 of the screen grid tubular ele- 'ment 24 to a pair'of lead-ins 34 sealed through the stem base 36. The front end of the focusing subassembly 18 is centrally supported in the neck It) by a plurality of spring fingers 38 fixed to a top aperture plate 40 of the accelerating electrode 28. Flexible conductors 42 connecting some of the lead-ins of the stem 36 to electrodes of the cathode-grid-apertured-plate subassembly 16 serve no support function for the electron gun 14. Entire support for the cathode-grid-apertured-plate subassemoly 16 is by virtue of its being mounted on the focusing subassembly 18.

FIGS. 2 and 3 illustrate in detail the novel construction of the electron gun 14 according to my invention. These figures show the complete cathode-grid-aperturedplate subassembly 16 plus the tubular part 24 of the screen grid cup 22 which is included as part of the focusing subassembly 18.

The cathode-grid-apertured-plate subassembly 16 comprises a pair of spaced parallel insulator plates 44 each having a' plurality of apertures therein. A U-sh-aped channel electrode support member 46 is provided with a pair of flanges 48 along its open side. A tubular control grid 50 is disposed within the channel member 46 and is provided with an electron beam aperture 52 facing out the open side of the channel 46. An elongated indirect ly heated cathode 54 is disposed within the tubular control grid 50 and includes on one flat surface 56 thereof electron emissive material coating 58 generally opposite the control grid aperture 52. A heater coil 60 is disposed within the cathode 54 for heating the cathode to thermionically emitting temperature. Both the channel support member 46 and the tubular control grid 50 are provided with a plurality of cars 62 on each end thereof which are received within the apertures 63 of the insulator plates 44 for mounting the channel support 46 and the control grid 50 therebetween. The cathode 54 is mounted directly within accommodating apertures 64- in the insulator plates 44 for maintaining in its desired spaced relationship with the control grid 50. Arcuate apertures 65 provided in the insulator plates 44 are not designed to receive electrodes for support thereof but simply to reduce interelectrode leakage as is Well known in the art.

The cathode-ingrid-apertured-plate subassembly 16 includes the plate-like portion Ztl of the novel 2-piece screen grid cup 22. The plate 2! preferably comprises a shallow cup-like circular part having a central electron beam aperture 66 therein, which is the screen grid aper ture. The screen grid plate 20 is mounted on the flanges 48 of the channel 45 across the open side thereof. Attached to the screen grid plate 20 is a cylindrical Wall portion 68 of a diameter to receive in mating relationship therewith the tubular portion 24 of the screen grid cup 22. Thus, the screen grid cup 2?; is formed by integration of the two subassemblies 16 and Iii together as is shown in FIGS. 1 and 3.

By virtue of the novel Z-piece screen grid cup construction, wherein the apertured plate portion 20 thereof is included as a part of the cathode-grid-apertured'plate subassembly, alignment of the screen grid and control grid apertures 66 and 52 can be made as a separate step from and before the two subassemblies are joined together. Thus, alignment is not only made easier but also more accurate since the two apertures are easily accessible and aligning procedures are not interfered with by the focusing subassembly 1%. For example, as shown in FIG. 4, a mandrel '70 can be suitably provided with a small diameter portion 72 for receipt in the electron beam apertures 66 and 52 of the screen grid and control grid, respectively. Before the screen grid plate 20 is fixed to the flange 48 of the channel support 46, the apertures 66 and 52 are aligned by use of the mandrel '79. With the mandrel in place, suitable welds are made to secure the screen grid plate 26 to the flanges 48.

Alignment of the screen grid and control grid apertures 66 and 52 can thus be made directly, as by using the mandrel it, rather than indirectly by use of additional aligning holes through these members. Since the electron beam apertures of the control and screen grid electrodes are openly accessible and not interfered with by a focusing subassembly, alignment is performed at close range. This also contributes to accuracy. Although not illustrated, it will be appreciated that the two apertures can be aligned optically instead of by use of the mandrel 7t and that the advantage of accessibility is especially useful for optical alignment.

Rigidity, and low cost of parts and fabrication procedures are other advantages obtained by virtue of the novel construction according to my invention. The novel l-piece channel-shaped electrode support member 46 results in an extremely rigid cathodegrid-aperturedplate subassembly 16 as opposed to prior art subassemblies which include two separate supports, one on either side of the tubular control grid 50. Not only are two support parts thus replaced by a single support part, but by virtue of the l-piece support, use of a strap sometimes employed by the prior art between separate screen grid supports to obtain some degree of rigidity is not necessary. Thus, three parts are replaced by one and at the same time a more rigid structure results which is, moreover, less costly to fabricate.

I claim:

1. An electron gun comprising first and second subassernblies, said first subassembly including a pair of spaced parallel insulator plates, a U-shaped channel member having outwardly extending flanges lying in a common plane at the free ends of the U arms along the open side thereof, said channel member being mounted between said plates axially perpendicular thereto, a tubular control grid member disposed in said channel and out of contact therewith and mounted between said plates, said control grid having an aperture in the side wall portion facing out of said channel, an elongated cathode mounted between said plates within said tubular control grid opposite said aperture, and a shallow cup having in its base a central aperture approximately equal in diameter to said control grid aperture, said cup being mounted across the top of said channel on said flanges with the exterior of its base in contact with said flanges and with its aperture axially aligned with said control grid aperture, said second subassembly including a plurality of axially aligned tubular electrodes mounted in fixed spaced relation along at least one insulator rod, an end one of said electrodes having its end remote with respect to the adjacent one of said tubular electrodes seated in said shallow cup of said first subassembly and fixed thereto to form therewith an integrated 2-piece centrally apertured cup electrode, whereby prior to the integration of said 2-piece electrode said apertures are accessible to be directly aligned by insertion of an alignment mandrel thereinto.

2. An electron gun comprising in axially parallel relationship a channel member, a tubular control grid within said channel, and an elongated cathode within said control grid; a pair of spaced parallel insulator plates by and between which said channel member, control grid, and cathode are supported axially normal thereto, an electrode plate having a short cylindrical sidewall mounted on said channel member across the open side thereof; said electrode plate and the side of said control grid adjacent thereto having aligned apertures of electron beam controlling size opposite said cathode; a tubular member mounted coaxially within said short cylindrical sidewall on the side of said electrode plate opposite said channel member and forming with said plate a 2-piece cup electrode havingv an apertured end wall; at least one insulator rod connected to said tubular member and extending axially parallel thereto; and at least one other electrode supported by said rod coaxially with said apertures, whereby in the fabrication of said gun prior to the mounting of said tubular member on said plate, said plate is unobstructed by said other electrode so that an alignment mandrel can be inserted directly into both of said apertures.

3. An electron gun comprising a pair of spaced parallel insulators to and between which are mounted a cathode, an apertured control grid, and electrode support means, a shallow cup member fixed to said support means and having a plate-like portion with a central aperture therein aligned with the aperture of said control grid and with the apertures substantially equal in size, a tubular element received co-axially within and fixed to said member on the side thereof opposite said control grid, and at least one other electrode insulatingly supported relative to said tubular element, said member and said element forming, respectively, the apertured end wall and tubular I Wall portions of a 2-piece cup electrode.

References Cited in the file of this patent 

1. AN ELECTRON GUN COMPRISING FIRST AND SECOND SUBASSEMBLIES, SAID FIRST SUBASSEMBLY INCLUDING A PAIR OF SPACED PARALLEL INSULATOR PLATES, A U-SHAPED CHANNEL MEMBER HAVING OUTWARDLY EXTENDING FLANGES LYING IN A COMMON PLANE AT THE FREE ENDS OF THE U ARMS ALONG THE OPEN SIDE THEREOF, SAID CHANNEL MEMBER BEING MOUNTED BETWEEN SAID PLATES AXIALLY PERPENDICULAR THERETO, A TUBULAR CONTROL GRID MEMBER DISPOSED IN SAID CHANNEL AND OUT OF CONTACT THEREWITH AND MOUNTED BETWEEN SAID PLATES, SAID CONTROL GRID HAVING AN APERTURE IN THE SIDE WALL PORTION FACING OUT OF SAID CHANNEL, AN ELONGATED CATHODE MOUNTED BETWEEN SAID PLATES WITHIN SAID TUBULAR CONTROL GRID OPPOSITE SAID APERTURE, AND A SHALLOW CUP HAVING IN ITS BASE A CENTRAL APERTURE APPROXIMATELY EQUAL IN DIAMETER TO SAID CONTROL GRID APERTURE, SAID CUP BEING MOUNTED ACROSS THE TOP OF SAID CHANNEL ON SAID FLANGES WITH THE EXTERIOR OF ITS BASE IN CONTACT WITH SAID FLANGES AND WITH ITS APERTURE AXIALLY ALIGNED WITH SAID CONTROL GRID APERTURE, SAID SECOND SUBASSEMBLY INCLUDING A PLURALITY OF AXIALLY ALIGNED TUBULAR ELECTRODES MOUNTED IN FIXED SPACED RELATION ALONG AT LEAST ONE INSULATOR ROD, AN END ONE, OF SAID ELECTRODES HAVING ITS END REMOTE WITH 